This invention relates to vulcanizable polychloroprene compositions. More particularly, it relates to vulcanizable general purpose W-type polychloroprene compositions having incorporated therein a .beta.-substituted diperoxyketal selected from the group consisting of 2,2-bis-(t-butyl peroxy) butane and 1,1-bis-(t-butyl peroxy)-3,3,5-trimethyl cyclohexane in the absence of an antioxidant.
Chloroprene elastomers are well known materials in the rubber art and useful elastomeric products must necessarily be vulcanized, i.e. "cured" by crosslinking. Heretofore, it has been considered necessary in order to achieve good aging vulcanizates to employ an antioxidant in conventional formulations of all types of chloroprene. It has now been found that vulcanizates of W-type chloroprene exhibiting highly desirable aging characteristics can be achieved without the need of employing an antioxidant in the curing thereof when the vulcanizable composition has incorporated therein a .beta.-substituted diperoxyketal selected from the group consisting of 2,2-bis(t-butyl peroxy) butane and 1,1-bis-(t-butyl peroxy)-3,3,5-trimethyl cyclohexane.
Diperoxyketals have been employed in the past for the curing of such materials as ethylene, dially phthalate/polyethylene glycol fumarate, and vinyl monomers. Illustrative patents disclosing the use of diperoxyketals in such curing systems include U.S. Pat. No. 2,650,913 which discloses the use of 2,2-bis-(t-butyl peroxy) butane for ethylene polymerization; U.S. Pat. Nos. 2,656,334 and 2,692,260 which disclose vinyl polymerization utilizing a combination such as dibenzoyl peroxide and 2,2-bis(t-butyl peroxy) butane; Netherlands application No. 6,403,775 (Jan. 25, 1965) which discloses high pressure ethylene polymerization using various bis-(t-butyl peroxy) ketals; U.S. Pat. No. 2,698,311 which discloses the curing of unsaturated polyester resins such as diallyl phthalate/polyethylene glycol fumarate using 2,2-bis(t-butyl peroxy) butane; German Pat. No. 945,187 which discloses the use of 2,2-bis(t-butyl peroxy) butane and 1,1-bis-(t-butyl peroxy)-3,3,5-trimethylcyclohexane as catalysts for a rubber vulcanizing process; U.S. Pat. No. 3,296,184 which discloses the vulcanization of olefin polymers and ethylene .alpha.-olefin copolymers with a peroxidic compound having a di-perketalic structure; U.S. Pat. No. 3,344,125 which discloses crosslinking a saturated synthetic rubber with a peroxide including 1,1-bis-(t-butyl peroxy)-3,3,5-trimethylcyclohexane; and U.S. Pat. No. 3,686,102 which discloses curing ethylenically unsaturated monomers with certain .beta.-substituted diperoxyketals such as 2,2-di(t-butyl peroxy)-4-methyl pentane.